In my copending application, Ser. No. 603,776 filed Aug. 11, 1975, entitled "Polyphonic Tone Synthesizer", now issued as U.S. Pat. No. 4,085,644 there is described an electronic keyboard instrument in which each key initiates a tone whose waveform is generated from digitally computed data. In copending application Ser. No. 619,615, filed Oct. 6, 1975, issued as U.S. Pat. No. 4,022,098 entitled "keyboard Switch Detect and Assignor", there is described a system for detecting the change of state of key-operated switches and causing a number of tone generation system to be assigned or unassigned in response to detected key state changes. Groups of key-operated switches, each group corresponding to the standard twelve keys in an octave, are sequentially scanned to detect a change in the state of the key switch as in each group. Information on the octave and keyboard of each depressed key and the assignment status of the key to a tone generator is stored in memory during an assignment mode. By having more than one tone generator, more than one tone can be generated at a time in response to more than one key at a time.
In the past various systems have been used in conjunction with electronic organs for generating complete chords in response to actuating a single key or manually controlled switch. So-called chord organs simplify the execution of more complex musical arrangements with a minimum of training. The present invention is directed to a digital circuit for implementing automatic chord generation in a digital computer organ with a keyboard switch detect and assignor circuit of the type described in the above-identified patent application.